Sushi Threatened As Popular Ingredient Biomass Halved Since 1950

A beloved ingredient used in sushi could soon completely disappear if overfishing is not managed, a new study has found.

The yellowfin tuna is a common ingredient in some globally popular dishes, not just sushi, but also sashimi, poke bowls and sandwiches.

However, the species is being over-exploited to such an extent—especially in the Indian Ocean—that it could soon disappear from these popular dishes, a paper published in Ocean and Coastal Management reveals.

The global biomass—weight of a given population in the water—of yellowfin tuna has decreased by 54 percent since industrial exploitation began in 1950. Now, it has come to light that the Indian Ocean has seen a huge drop, with the species declining by 70 percent in the past seven decades, the study said.

Kristina Heidrich, lead author of the study and a Ph.D. candidate at the Sea Around Us—Indian Ocean, part of the School of Biological Sciences at the University of Western Australia (UWA), said in a press release that recent years have seen a greater decline.

“Biomass continues to decline everywhere except for stabilizing trends in the Western Pacific Ocean, prompted by management interventions,” Heidrich said.

Dirk Zeller, co-author of the study and director of the Sea Around Us—Indian Ocean added that in most places, fishing of yellowfin tuna has “surpassed the maximum sustainable yield.”

Overfishing has long been a problem for the species, to the degree that it is classed as Near Threatened by the International Union for Conservation of Nature.

The researchers findings were reached by assessing tuna biomass changes from 1950 to 2020 using multiple methodologies, including more than 950 records of yellowfin tuna taken from “Baited Remote Underwater Video Systems (BRUVS ).”

“The data collected with BRUVS provided a more holistic and fisheries-independent picture of the pelagic community and the status of the populations, which can complement fisheries-dependent data and analyses,” Jessica Meeuwig, another co-author of the paper and director of UWA’s Marine Futures Lab, said in a statement.

“These fisheries-independent BRUVS data suggest that, since 2014, yellowfin tuna in the Indian Ocean are the least common, least abundant, have the lowest biomass, and are the smallest yellowfin tuna in the existing dataset,” she said.

A catch reduction of 30 percent in the Indian Ocean is urgently required, to both “halt and reverse” the decline in yellowfin tuna, according to Heidrich.

According to the International Seafood Sustainability Foundation, 61 percent of all tuna stocks are at a healthy level of abundance but 13 percent are considered over-fished.

The United Nations Food and Agriculture Organization reports that the majority of tuna stocks are “fully exploited,” meaning there is no way their fisheries could expand. Some are even at risk of collapse.

“Beyond yellowfin tuna fisheries contributing more than $16 billion to the global economy yearly, the species is an apex predator that plays a critical role in the functioning, productivity and overall health of marine ecosystems,” Daniel Pauly, a fellow co-author of the study and principal investigator of the Sea Around Us initiative at the University of British Columbia, said in a statement.

“The risk of population collapse is high if current management does not adapt,” he said. “Stringent management constraints must be implemented to reduce overall fishing capacity, rebuild overfished populations, and reduce the collateral damage these fisheries cause to other species such as sharks.”

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